Although you can set Windows Explorer to show you the thumbnails of all your pictures, it usually makes it slower to browse through different folders. Additionally it also creates multiple thumbs.db files in each folder and all such files may take up considerable amount of disk space. An alternative to thumbnail preview feature of Windows is adding an image preview in the right-click menu. This can be done easily using the free FastPreview shell extension. It adds an Image Preview in the right-click context menu so that when you right-click on an image file, you see its preview right inside the context menu.